A novel control strategy for the seamless transfer of microgrids based on disturbance observer

This paper presents a novel seamless transfer strategy for microgrids (MGs) that enables both grid-connected and islanding modes, with no need of forced controller switching between different controllers and with improved performance in both reference tracking and disturbance attenuation. A unified control structure based on droop technique is utilized to generate the voltage and frequency references, accommodating all operation modes. Alternatively, the dynamical feedforward with reference model control and disturbance observer are introduced into the cascaded voltage-current control, which not only estimates and compensates the influences of power fluctuation as well as model uncertainties timely, but also provides the perfect reference tracking capability. Then the detailed analysis on the deduced mathematical model of inverter is carried out, and the superiority of the proposed strategy is demonstrated in tracking performance, disturbance attenuation and robustness. Simulation and experimental results show that the harmful transients during the operation mode transition can be effectively eliminated with the overall dynamic performance improved so that the effectiveness of the proposed control scheme is verified.